In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
An endless track drive is made up of a number of components such as links, track pin bushings, rollers, track pins and shoes, as well as a sprocket wheel. U.S. Pat. No. 2,271,172 is illustrative of such devices. The content U.S. Pat. No. 2,271,172 is incorporated herein by reference, in its entirety.
The components of endless track drives are subjected to very severe operating environments. For example, debris, soil, rocks and so forth can enter the track and undercarriage of a track-type machine, such as a crawler tractor, during operation. These materials can subsequently accumulate between the engaging surfaces of the track pin bushing and the drive sprocket teeth, pack into the track and tighten the track tension, and/or directly grind, wear, pit, scratch or crack the surfaces of the components. Additionally, the components are subjected to corrosive conditions, which can further exacerbate the above wear mechanisms.
Conventional sprocket wheels are typically formed from hardened steel materials. For example, steel sprocket wheels may have a surface treatment such as carburization, nitriding or other surface hardening procedure applied thereto. However, such surface-hardened steel sprockets still pose certain drawbacks, as such materials and methods can still result in a relatively short service life.
For example, sand can be harder than even surface-hardened steel, thus resulting in abrasion of the component. The above-mentioned surface treatments are not cost-effective solutions for preventing corrosion. Formation of the sprocket gear from a more expensive highly-alloyed steel composition is also not a fully acceptable solution because even hardened highly-alloyed steels are susceptible to abrasion by contact with sand. Moreover, such highly-alloyed steels are not economical.
U.S. Pat. No. 5,933,955, the entire content of which is incorporated herein by reference, discloses a method of making a drive sprocket which involves water-jet machining the sprocket teeth so as to leave the homogeneity of the composition and structure of the metal material unaffected, followed by selective surface hardening.
U.S. Pat. No. 6,414,258, the entire content of which is incorporated herein by reference, describes a technique for forming a weld overlay on a sprocket and/or bushing surface. According to this patent, an arc electrode is applied to a base metal, forming a “weld pool” on the surface thereof. Cemented carbide particles are then fed into the weld pool, which subsequently solidifies, leaving a bead-like formation on the surface of the part. This approach has certain disadvantages. The above-described procedure is tedious, time-consuming and costly. The treated surface resulting from this procedure is a relatively rough sinusoidal surface. Moreover, the cemented carbide particles are relatively expensive materials.
U.S. Pat. No. 5,879,743, the entire content of which is incorporated herein by reference, discloses a process for hardfacing a machine component by applying a slurry containing an alloy to the surface of the base metal, then fusing or metallurgically bonding the coating to the base material. The process described in this patent is not specifically adapted to produce an improved sprocket wheel component.
U.S. Patent Application Publication No. 2003/0168912 A1, the entire content of which is incorporated herein by reference, describes a process for applying a slurry coating to operative surfaces of track bushings, then fusing or metallurgically bonding the coating to the base metal of the component. Testing of track bushings treated as described therein has demonstrated that this technique is a cost-effective method of increasing wear and corrosion resistance of these components.
However, track bushings contact sprocket gear wheels in the above-described endless track drive mechanisms. The service life of conventional sprocket gear wheels are not seen as being able to match that of the above-described improved bushings. Thus, the overall service life of the endless track drive mechanism is unnecessarily limited by current sprocket wheel constructions.
Therefore, there is a need to provide a sprocket wheel with improved service life and performance characteristics.